The invention concerns a monobloc stopper rod to control the outflow of metallurgical melt containers.
Such a stopper rod e.g. disclosed in EP 0 721 388 B1 consists of a cylindrical stopper rod body made of a fire-resistant, carbon-containing material. The stopper rod body has a section in a base part to receive a guide rod, and it has a cap-like section at its end.
With the aid of the cited guide rod, the monobloc stopper is guided away in an axial direction from an associated outlet in the metallurgical container when the metal melt is to flow out, or lowered to the outlet to seal it if the flow of molten metal is to be reduced or interrupted.
It is known that chemical reactions can cause encrustation which clog the outlet and make it difficult or impossible to control the melt flow.
To prevent this problem, EP 0 721 388 B1 suggests a generic stopper plug where the stopper plug body is completely or partially covered with a layer consisting of 4-9 weight percent carbon and at least one sintering promoter. The surface layer compresses after being heated above 1,000xc2x0 C. and becomes impervious to gas. The stated thickness of the layer is less than 10 mm. According to an exemplary embodiment, the layer is limited to the nose-like section of the stopper rod.
Such a stopper rod is difficult to manufacture, especially when it is to be isostatically pressed as suggested in EP 721 388 B1; the cited surface layer on the nose-like section is difficult to produce in a corresponding press mold. In addition, the layer can easily fracture when it is used.
The problem of the invention is therefore to improve a stopper plug of the cited type so that it can be manufactured in a simple process, reliably prevents the cited encrustation, and allows flawless use as a control organ in metallurgical melt containers.